It's really hard to parse your requirements, Could you out-line the datastructure in code, please?
Then I'll explain what I have today, and how I want to improve it. First of all, to add a bit of context, I'm working on a 3D engine. There are a lot of "resources", being Mesh, Character, Camera, Material, etc. I have a very classic class hierarchy around these: * Resource: base class, holds the ID of the element (std::string) * Material: directly derives from Resource * GeomElem: derives from Resource, that is the base class for geometric elements, mainly holds the PRS matrix * Camera: derives from GeomElem, the PRS matrix is the point of view for the current frame * RenderElem: derives from GeomElem, intermediate class for geometric elements that will be rendered, holds a pointer to a Material and a bounding sphere because from this class we're talking of "volumetric elements" * Mesh: derives from RenderElem, holds triangles, points, etc. * Character: derives from RenderElem, has a bone hierarchy for skeletal animations And so on. As you understood, Resource is my class A, Material my class B, RenderElem my class C, Mesh my class D, and Character my class E. On these resource, I want to be able to query them by ID, delete them, add them, etc. And I want to be able to provide the final class type (like GetResource<Mesh>("MyMeshName") to have a faster lookup, or an intermediate class, like RenderElem, and have a lookup only in the RenderElem derived classes. That last feature with the intermediate class is what I am missing at this point. For the implementation details of my current version: * I have a simple wrapper to holds all my strongly typed resources, called ResourceHolder, that contains a std::map<const std::string *, Resource *>. The key is a pointer to the std::string contained in the value, that is the actual name of the Resource. * At startup, I "register" all my resources types using a std::string as type ID. I have a singleton class: template <class T> struct TypeToString { std::string m_Name ; } ; and I instanciate that template for all my Resource derived classes. This is useful for the next point along with another structure that helps me construct my correctly typed Resources at loading time. * Then I have a container of ResourceHolder, that is called ResourceManager, that holds every resource for the application. Everything the developer can do is implemented in ResourceManager. Mainly the GetResource function has a template override that accepts the type as template argument. This way, I can use the TypeToString singleton to get the std::string corresponding to the type, and thus find the ResourceHolder containing all the resources of this type. Then I lookup using the name of the resource in the correct ResourceHolder to find the desired Resource. If I don't use the template version of GetResource, then I will iterate over ALL the ResourceHolders contained in the ResourceManager. So, I want an über-container that will perform all these lookups using no type, the final type, or possibly the intermediate type. And I'll need access to views of these sub-containers, because often I need to use some for_each algorithm on a specific type (ask all Materials to load their textures, ask all RenderElems to prepare for rendering,...). This is something I can perform only on final types at this point. I don't like my structure, and would be pleased to get rid of it in benefit of a better one. But if I don't find a way, I'll implement some kind of TypeToString hierarchy so that I'll be able to know all derived types from an intermediate one. As a future improvement, I'll have to use some kind of "scope" in this structure to sort Resources by "levels" (and I'll have to get rid of the std::string as IDs too). Any clue on that improvement would be mostly appreciated too. Hope this clears things up, SeskaPeel. -----Message d'origine----- De : boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] De la part de Thorsten Ottosen Envoyé : mercredi 26 avril 2006 18:29 À : boost@lists.boost.org Objet : Re: [boost] Class views on an associative container SeskaPeel wrote:
Hi list,
I'm looking for a "multi-class container", with access to sub-containers of elements depending on their class. All elements are derived from the same base class, and I want to have "views" of containers of final classes, or even intermediate classes. This container would be associative, like a map.
As instance if I have
// Base class
class A {} ;
// Intermediate classes
class B : public A {} ;
// Final classes
class C : public B {} ;
class D : public B {} ;
class E : public A {} ;
I want a container that can hold any A-derived class,
That is easy.
on which I could have views of sub containers of class C, D or E, and even a sub container of intermediate class B.
-Thorsten _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost